This invention relates to fluid springs or actuators designed for use with fluids including incompressible and compressible fluids. In particular, the fluid actuator is of the rolling lobe form in which a flexible membrane rolls axially on a piston peripheral surface.
Conventional airsprings utilize a flexible, air-impervious membrane which is fastened in some manner on one end to a piston and on the opposite end to an upper retainer which forms, between the three elements, an internal working cavity for the enclosure of the designed fluid. The attachment of the rubber flexible membrane to the rigid components is a long standing source of leakage and failure of airsprings and air actuators. A flexible member may be used which includes a bead structure at its extreme ends for attachment in suitably formed bead seating areas of the rigid members. In other common configurations, the extreme axial ends of the flexible member are banded, swaged or otherwise compressively engaged against the outer periphery of the rigid membrane to effect an airtight seal at both ends. During service of the conventional beaded and swaged airspring structure, failure or air leakage occurs most commonly at the interface between the rigid member and the flexible membrane.
It is well known from tire technology that a toroidally shaped elastomeric composite structure exhibits unparalleled ability to withstand high internal pressure due to the uniform distribution of force throughout the toroid shape, enabling the bias laid reinforcement fabrics to uniformly distribute the force over the smoothly curving toroidal surface. A tire, however, is an open toroid with the automobile rim or wheel closing the toroid through the use of bead structures in the tire. This invention utilizes a closed toroidally shaped membrane which can withstand high internal pressures. This closed toroid also exhibits the marked advantage that there are no seals and no sealing required for construction and operation of the airspring. In addition, the fluid actuator of the invention provides for a central passageway through the entire axial length of the fluid actuator through which any shaft, shock absorber or other desired member may pass. This configuration is especially useful for such applications as a clutch where the drive shaft may pass through the actuator. Brake applications are also particularly well suited, since a central hub or axle may advantageously pass through the central passageway. A third aspect of the applicant's invention is the formation of dual concentric rolling lobes which result from an annular piston which moves axially into and out of the closed toroidal diaphragm to form an inner rolling lobe and an outer rolling lobe on the inner and uter surfaces respectively of the annular piston. This configuration has the advantage of higher lateral spring rate and stability than standard airsprings. It results in lower axial spring rate than simple bellows airsprings. It can contain a center shaft, axle, shock absorber without any need for airtight sealing.
The fluid actuators of this invention have the advantage that no airtight seals are required on a rolling lobe type spring assembly. Further, the construction of the flexible membrane is simple due to the closed toroidal form of the diaphragm. In addition, there is no obstruction in the center of the airspring or actuator and a structural element of the apparatus in which it is being utilized may pass through the central passage.